The Blade of Ahn-nunurta

The weapon listed here is counted as a "Power" and "Force" weapon for those rules that affect such weapons.

Any Psyker with a weapon or ability with this special rule may choose to make a Psychic check before making any attacks with that weapon or resolving the ability. If the Check is successful then the Strength value of any attacks made is doubled. If the Check is failed then Perils of the Warp is resolved targeting the unit containing the model that failed its Check. If the Psyker survives Perils of the Warp then it may attack as normal.

A model attacking with this weapon never receives +1 Attack for fighting with two Melee weapons (see page 177).